DEPOSITIONAL SETTING AND HISTORY OF THE TAR SPRINGS SANDSTONE (UPPER MISSISSIPPIAN), SOUTHERN ILLINOIS l

ABSTRACT: The Tar Springs Sandstone (Upper Mississippian) crops out in a thin belt around the southern margin of the Illinois Basin. The formation is composed of fine-grained, well-sorted quartz arenites and sublitharenites. Four facies recognized by their lithologies, sedimentary structures, geometries, and geo-graphical locations, comprise the Tar Springs Sandstone. These facies and their dominant characteristics are: 1) Facies A, cross-bedded sandstone; 2) Facies B, horizontally bedded sandstone; 3) Facies C, flaser-and lenticular-bedded sandstone and shale; and 4) Facies D, interbedded sandstones and shales. The Tar Springs Sandstone represents deposition by prograding fluvial-deltaic and paralic sedimentary environments. Specific depositional environments are fluvial and distributary channels (Facies A), shore-face and foreshore (Facies B). tidal flats (Facies C), and pro-delta, interdistributary bay. floodplain, and destructional bars (lower, middle, and upper Facies D). The distribution of the deposits reflects a longshore change in marine processes from wave-dominated in the southeast to tide-dominated in the northwest. This suggests ~hat here was either a change in bathymetry or coastal configuration that resulted in diminished wave energy and an enhanced tidal regime in a longshore direction away from the major sediment sources. Interpretations of the depositional history of the Tar Springs Sandstone suggest the following sequence of events. Fluvial and distributary channels traversed a broad coastal plain and built high-constructive lobat